Reproduce this behavior should be simply: send a request with two content type, give a quality factor to some of mime type and it will be returned. This happens in some specific scenario: It only happens when you don't have a MediaType declared in the resource method; So, giving the following JAX-RS method: @Path( "resource" ) public class Resource { @GET @Path( "other" ) public Response other() { return Response.ok( "other invoked" ).build(); } } You can simply reproduce it: $ curl -H 'Accept: application/json;q=0.3, application/xml;q=0.2' -D - http: //localhost:8080/01840977-reproducer/resource/other HTTP/1.1 200 OK Connection: keep-alive X-Powered-By: Undertow/1 Server: JBoss-EAP/7 Content-Type: application/json;q=0.3 Content-Length: 13 Date: Mon, 20 Nov 2017 02:22:31 GMT